Gait deviations

Gait deviations are nominally referred to as any variation of

Over 185,000 amputations occur annually, with approximately 86% of incidents being lower-limb amputations.^[4] The majority of cases are reportedly caused by vascular disease (54%) and trauma (45%).^[5] Lower-limb amputees are further categorized by where the amputation occurs with respect to the knee joint. However, 34.5% of individuals with an initial foot or ankle amputation experience a progression of symptoms leading to subsequent amputations at higher levels of limb loss.^[6] Out of these reamputation cases, diabetic patients had a higher likelihood of requiring further amputations, regardless of initial amputation location.^[6] The rate of amputation has decreased significantly with the introduction and optimization of revascularization to combat vascular disease.^[7] An increasingly studied trend in amputation rates is the gender disparity of women receiving more surgical revascularization treatments and less amputations than male counterparts.^[8][9]

Transtibial

An amputation between the knee and ankle joints transecting the

Unlike transtibial amputations, transfemoral amputations occur between the hip and the knee joints, along the length the femur. Therefore, the patient's residual limb is controlled solely by the hip joint. Implementing a prosthetic leg requires the user to mechanically control the behaviors of the prosthetic knee and ankle joints through gross adjustments of the hip, rather than the finer and more precise movements of the missing joints.^[11] Simple tasks such as walking on level ground, sit-to-stand transfers, and climbing stairs^[12] require complex alternative muscle activation patterns^[13] because the amputee cannot generate a moment about the prosthetic knee.^[14] This poses a problem when knee flexion is required, especially during the transition from the stance phase to the swing phase. Transfemoral amputees, on average, have more variability in stride length and walking speed, more asymmetry in temporal measures between limbs, and have an overall slower walking speed than transtibial amputees.^[15]

Compensatory Behaviors

Unimpaired

Bodily involvement

Before microprocessor-controlled prosthetic joints, the major findings were that the most noticeable movements could be seen in the

Stride length refers to the distance in the direction of forward motion that is between heel strikes of successive footfalls or steps. During the gait cycle, amputees have characteristically shorter time spent in the stance phase on the prosthetic limb compared to the intact limb.^[23][24][25] Stride length is arguably the most visible of the changes in amputee gait because it creates such an asymmetry between the intact and impaired limbs. However, the shorter stance time may help the amputee compensate for the greater margin of error of the prosthetic limb, and several sources suggest the shorter strides are beneficial towards maintaining a straight walking path.^[25]

Step width

Step

The compensatory behaviors listed above describe the observable differences in ambulation between amputees and able-bodied individuals. The following gait deviation measurements quantify differences using gait analysis and other tests that typically necessitate specialized instrumentation or clinical environments.

Metabolic cost

Energy expenditure is commonly used as a measure of gait quality and efficiency. Human metabolic rates are usually recorded via measuring the maximal oxygen consumption (VO₂ max) during controlled incremental exercise under observation. Treadmills are used for gait analysis and standard walking tests. Able-bodied and athletic individuals on average have smaller metabolic costs than impaired individuals performing identical tasks.^[39][40]

The values from a theoretical model^[41] and experimental analyses^{[38][42][43][44][45]} are listed below:

• Transtibial amputees experience 9-33% increase
• Transfemoral amputees experience 66-100% increase

Another source^[46] compiled a list of average metabolic cost increases categorized by amputation location and by cause of amputation:

• Transtibial (traumatic) amputees experience 25% increase^[47][48][49]
• Transtibial (vascular) amputees experience 40% increase^[47][48][49]
• Transfemoral (traumatic) amputees experience 68% increase^[50][18]
• Transfemoral (vascular) amputees experience 100% increase^[50][18]

Comfortable walking speed

Although heavily related to the metabolic cost and overall

Similar to decreased stride length and increased step width, lateral sway is generally postulated to be an indication of gait instability. The gait naturally widens to account for a greater instability or external perturbations to balance. Step variability is also related to balance and lateral stability. The variability in length and width of steps can be attributed to a level of responsiveness to external factors and perturbations, or an indication of inherent instability and lack of control.[56] This has been a common discussion in analysis of elderly gait as well.^[30][29] Internal rotation is a culmination of measures of the hip and knee joints as well as the pelvic rotation and obliquity during gait. Typically, this has to be measured through motion capture and ground reaction force. Individual parameters can be calculated with inverse kinematics.^[18]

Influential Factors

Across the field of research, many studies are focused on assessing how different factors can influence the overall gait of amputee subjects. The following list shows examples of factors that are believed to influence the gait characteristics of lower-limb amputees:

• Weight of prosthesis
• Distribution of weight
• Alignment of components
• Overall fit of prosthesis

Prosthetic weight and distribution

A common trend in modern technology is the push to create lightweight devices. A 1981 collection of studies on amputees showed a 30% increase in metabolic cost of walking for an able-bodied subject with 2-kg weights fixed to each foot.^[57] Correspondingly, transfemoral prostheses are on average only about one third of the weight of the limb they are replacing. However, the effect of added mass appears to be less significant for amputees. Small increases in mass (4-oz and 8-oz) of a prosthetic foot had no significant effect^[58] and, similarly, adding 0.68-kg and 1.34-kg masses to the center of the shank of transfemoral prostheses did not alter metabolic cost at any of the tested walking speeds (0.6, 1.0, and 1.5 m/s).^[59] In another study, muscular efforts were significantly increased with added mass, yet there was no significant impact on walking speeds and over half of the subjects preferred a prosthetic that was loaded to match 75% weight of the sound leg.^[60] In fact, it has been reported in several articles that test subjects actually prefer heavier prostheses, even when the load is completely superficial.^[61]

Alignment and fit

Initial alignment of a prosthetic leg is conducted by a

Transtibial

In transtibial amputees, the adjustment of the foot is highly influential to gait changes. Proper alignment of the prosthetic foot about the ankle joint causes metabolic cost^[48] and gait symmetry at the anatomical hip and knee joints to improve, with hip flexion-extension motion being the most sensitive to alignment.^[62] Excessive rotational misalignment of the foot is compensated by internal rotation of the residual hip joint.^[63] Proper alignment of the transtibial prosthesis socket significantly reduced the loading on the intact limb during an 11-meter walk test, indicating that a misaligned limb could have drastic long-term consequences on the sound side of the body.^[64]

Transfemoral

Systematic changes to transfemoral prosthetic alignment altered the flexion-extension behavior of the hip, changing fore-aft ground reaction forces and the antero-posterior moments at the knee and ankle joints.

• Gait training
• Rehabilitation engineering
• Biomedical engineering

References